Hello,

I have to build a 555 timer circuit for a school assignment based on this schematic:

I set up a prototype circuit on breadboard and it works just fine. The problem is that after I've built my PCB (which checked out for continuity) and soldered the components, the circuit does not work as intended. The LED turns on but it does not blink.


I've tested all my components for correct values (I'm using a 200 Ohm for R3 because I don't have a 220, though I don't think that matters), tested my capacitor for a short circuit, and even replaced my IC twice. At this point I have no idea what the problem is, though I'm assuming it may have something to do with my PCB layout. I know my solder joints aren't the best, but they are definitely conducting. And in the picture it looks like R2 and pin 7 of the IC aren't connected, but they are (the copper trace connecting R2 to pin 7 ripped off the board, so I had to solder the lead of R2 directly to pin 7).

I would greatly appreciate some help troubleshooting this because I've tried everything that, to my knowledge, could fix the issue.

Thanks,

-D

MOD: Tidied your images.E

 

If you expect us to help, you are going to have to provide pictures that are a lot clearer.

Bob

 

Erm, isnt your 555 plugged in the wrong way around?

 

hi dp,
Welcome to AAC.
Check for a track break,
E

 

If you expect us to help, you are going to have to provide pictures that are a lot clearer.

Bob

What is unclear about the pictures? The PCB is marked with component labels and pin labels on the IC. I'll gladly upload a new picture with whatever other specifications you require.

-D

hi dp, I have adjusted your images.E

 

hi dp,
Welcome to AAC.
Check for a track break,
E
View attachment 170955

Hi, thank you!

There's continuity between pins 2 and 6, just re-tested.

 

Erm, isnt your 555 plugged in the wrong way around?

On the bottom it's a mirror image of the IC, so it goes from pins 8-1 counterclockwise starting from the bottom right.

 

But it looks like your 555 time chip is plugged in with pin 4 & 5 toward the battery side of your PCB.. which is not according to your annotated underside photo of the PCB.

 

There's continuity between pins 2 and 6, just re-tested.

OK,
Is the cap the correct way around.? its hard to see the coding.
E

 

But it looks like your 555 time chip is plugged in with pin 4 & 5 toward the battery side of your PCB.. which is not according to your annotated underside photo of the PCB.

Wow, yes it is! What an obvious mistake! Haha, thanks for the help.

 

hi,
I agree with @pmd34. check the orientation
E